Numerous developments that employ cell-culture techniques in medical technology, pharmaceuticals, and the like are currently underway. As a specific example, techniques for culturing cells that express the characteristic functions of biological tissues and organs are being applied to drug toxicity tests, evaluations of endocrine disruption effects, the screening of new drugs, and other techniques, wherein the cultured cells are used as an in vitro model of the tissue or organ.
Such cell-culture techniques generally involve attaching and then culturing cells in a monolayer (i.e., in two dimensions) on a planar substrate on which collagen or another cellular-adhering material has been coated. When primary hepatocytes or the like isolated from the liver of a living organism, for example, are cultured in such a monolayer, the cells in such instances lose the characteristic liver functions or die off in an extremely short period of time.
By contrast, it has been discovered in recent years that the survival and characteristic liver functions of primary hepatocytes can be maintained for longer periods of time by culturing the cells in cellular tissues, which are aggregates wherein the cells are connected one another in three dimensions, instead of culturing the cells in a monolayer.
An example of a conventional method for forming such hepatic cellular tissue is disclosed in Patent Document 1, wherein a specific growth factor is added to the culture medium, whereby spherical hepatic cellular tissues are formed within the pores of a polyurethane foam.
Patent Document 2 discloses the formation of hepatic cellular tissue on a surface that is coated with a polymeric material that is composed of a monomer containing phenylborate, a monomer containing an amino group, and a 2-hydroxy-ethyl methacrylate copolymer.    [Patent Document 1] Japanese Laid-open Patent Publication No. 10-29951    [Patent Document 2] Japanese Patent Publication No. 3020930